Defining an object in an image is a common task in digital image editing. Generally, this task is referred to as selecting an object. There are a variety of reasons for selecting an object in an image. For example, a user may desire to copy the object elsewhere or to composite the object with another image in order to create a new image. Selecting an object also has the effect of restricting an image editing action to the selected region. Thus a tool or filter may be applied to the selected region to modify it in some way without altering the rest of the image. Selecting objects in images is, therefore, a common and frequently performed task.
Accordingly, digital image editors contain various tools for making selections of one or more objects. For example, a selection may be made in the form of straight line segments joining click points made by a user along an object boundary, as for instance with the Point to Point Selection tool in JASC® Paint Shop™ Pro®” (available through JASC Software®, Inc., Eden Prairie, Minn.). While it is quick to use, the disadvantage of this tool is that the straight segments may not accurately conform to the borders of the object. Alternatively, a selection may be traced along a boundary of an object, such as with the Freehand Selection tool of Paint Shop Pro. However, this boundary tracing can be a tedious and time-consuming task for objects with complex boundaries.
A variant of this technique is to trace the border of an object with a spline based curve such as is provided by the Pen tool of Paint Shop Pro. This technique has the advantage that any tracing errors may be corrected after the fact by editing the curve. However, this editing is itself time-consuming and requires some understanding on the part of the user.
Objects may also be selected according to color similarity, for instance by using the Magic Wand tool of Paint Shop Pro. This technique, however, is more appropriate to simple graphics than to photographed objects, which may contain a multiplicity of colors including some colors that are present in non-object areas.
Yet another alternative involves painting a selection onto an image, for example using the Edit Selection mode of Paint Shop Pro. While convenient in many cases, this method may be slow for complex objects and may require frequent changes in brush size to conform to the size of object features.
A growing group of digital camera purchasers are encountering digital image editing for the first time. As novices, they do not have the practiced facility with selection tools possessed by experts. There is, therefore, the need for new selection tools that provide a combination of speed and ease of use on the one hand and accuracy in delineating objects on the other, with which even a non-expert can achieve good results.
Consumer digital photographs can pose particular problems for selection tools since the consumer may not be a skilled photographer. Images are often of everyday scenes containing cluttered backgrounds and poorly lit subjects. Frequently, edges of objects in the scene are not well defined, such that decisions about the true boundary location of an object are hard to make. Consequently it is desirable that a new selection tool should not be dependent solely on image gradients for defining the boundary of an object but should also use other image information.
While it advantageous for any new selection tool to automate as much of the selection process as possible to assist the user, the tool should also offer sufficient flexibility to allow the selection to be placed exactly where desired. Excessive automation can be a drawback since incorrect placement of a selection can frustrate the user. This is especially true in the case of cluttered scenes, where only a human with understanding of the scene can determine the correct object or objects of interest by using knowledge about the shapes of real-world objects that is not encoded in the image. Various systems and methods described herein provide, among other things, a selection tool that meets these criteria.